The leukotrienes constitute a group of locally acting hormones, produced in living systems from arachidonic acid. The major leukotrienes are Leukotriene B.sub.4 (abbreviated as LTB.sub.4), LTC.sub.4, LTD.sub.4 and LTE.sub.4. The biosynthesis of these leukotrienes begins with the action of the enzyme 5-lipoxygenase on arachidonic acid to produce the epoxide known as Leukotriene A.sub.4 (LTA.sub.4), which is converted to the other leukotrienes by subsequent enzymatic steps. Further details of the biosynthesis as well as the metabolism of the leukotrienes are to be found in the book Leukotrienes and Lipoxygenases, ed. J. Rokach, Elsevier, Amsterdam (1989). The actions of the leukotrienes in living systems and their contribution to various diseases states are also discussed in the book by Rokach.
The ring system of the compounds of the present invention, thiopyrano[2,3,4-c,d]indole, is novel; that is, it has not been described in the prior art. A few derivatives of the natural product chuangxinmycin, which contains the thiopyrano [4,3,2-c,d]indole ring system, have been described as showing antibiotic and anticancer utilities. However, in addition to being isomeric with the present ring system, the substitution pattern is very different. The compounds of the present invention have complex substituents at positions 2 and 6, whereas such substitution is for the most part absent or very simple in the thiopyrano[4,3,2-c,d]indoles described. The following structures and references are illustrative of the compounds in the prior art. ##STR2##